Tips

BFS

When to use

• find shortest path: in matrix / from A to B / from one word change to another

Improve

• two end BFS, using two queues, one starting from the beginning, one starting from the end
• e.g., word ladder

DFS

• think about which traversal you want to use
• recursion is easier, iteration needs to use stack

Helper funciton

• use helper function when input or output needs to be different from the original method
• use global variable is easier to update the value
  • how to avoid using global variable
    • use ReturnType class, if needs to return multiple values
    • return result value from the bottom
• Divide and Conquer: bottom-up solution
  • divide the problem into small problem that can be implemented on every node
• exit condition
  • when node == null, when node is leaf node
  • when to return true and when to return false

Improve

• use memorization table / hashmap
• build a signature, and put it into hash set

Visited matrix

• don't forget to label the first element as visited before going into the while loop
• label child elements as visited before adding into the queue
• to avoid using it, you can update the visited elements to a new value